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#15060607
If you're heading at half the speed of light (relative to us and the black hole) towards a billion solar mass black hole and you are about 300 thousand kilometres from the event horison of said black hole. Approximately how long can we expect you to survive?
#15060667
Rich wrote:Approximately how long can we expect you to survive?

The instant you entered the black hole, reality would split in two. In one, you would be instantly incinerated, and in the other you would plunge on into the black hole utterly unharmed.

[...]

In fact, in a big enough black hole, you could live out the rest of your life pretty normally before dying at the singularity.


BBC Earth, The Big Question
#15060681
ingliz wrote:The instant you entered the black hole, reality would split in two. In one, you would be instantly incinerated, and in the other you would plunge on into the black hole utterly unharmed.

Not strictly correct. In general relativity, there is only ever one reality. I presume what they mean is that, from the viewpoint of a distant observer, the rate at which time passes on your spacecraft would appear to slow down and the light from your spacecraft would redshift as you approached the event horizon, eventually appearing to wink out of existence as you crossed over. From your own point of view, however, nothing untoward would seem to happen as you crossed over the event horizon; there would be no 'bump' or anything to tell you that, from henceforth, you were doomed....

In fact, in a big enough black hole, you could live out the rest of your life pretty normally before dying at the singularity.

That is correct.
#15060936
Rich wrote:Approximately how long can we expect you to survive?

The "we" part was carefully worded. As far as I understand it from our view point you will never reach or at least go beyond the event horizon. So at least from this simplest analysis, you will be immortal.

What happens from your point of view is less clear. Its normally differential gravity that spaghettifies you before you reach the event horizon, but as said this is not the case for a billion solar mass black hole. Will the gravity differential continue to increase as you move inwards the centre of mass of the black hole? But then there's the question of the expansion and contraction of the black hole.

If you can not reach the event horison, from our perspective, even if we watch for eternity, what happens if as we observe, the black hole collects more mass and therefore the event horison will expand beyond the point that you were at on the surface of the old event horison. And what happens if we keep watching for a really long time, into the heat death of the known universe and the size of the event horison starts to contract due to the Hawking radiation.
#15060950
Rancid wrote:Aren't we currently in a black hole?

You could regard the universe as a whole as a black hole (hey, that rhymes! :D ) if you really wanted to, but since we can't define what (if anything) exists beyond the universe's boundaries, it's pretty much meaningless.
#15060962
late wrote:No, a teaspoon of black hole would weigh more than Mt Everest.

All of that mass is concentrated at the singularity, @late, which is infinitesimally small. Inside a black hole, it's almost entirely just empty space.
#15060975
Potemkin wrote:All of that mass is concentrated at the singularity,

But is is? my understanding (far from perfect) is that space-time is so bent that matter hasn't had enough time to cross the event horison let alone reach the singularity. Although much of the mass of a black hole will be inside because it reached the black hole when it was less massive and hence had a much smaller event horison. And anyway I thought most physicists didn't believe in singularities finding them incompatible with quantum mechanics.
#15060981
Rich wrote:But is is? my understanding (far from perfect) is that space-time is so bent that matter hasn't had enough time to cross the event horison let alone reach the singularity. Although much of the mass of a black hole will be inside because it reached the black hole when it was less massive and hence had a much smaller event horison. And anyway I thought most physicists didn't believe in singularities finding them incompatible with quantum mechanics.

Singularities are not merely incompatible with quantum mechanics, they are incompatible with general relativity itself, the very theory which predicts their existence. Infinite density? Infinite curvature of space-time? Nobody really believes that. But nobody has a better theory (so far).

But to address your first question: space-time at the event horizon of a billion solar mass black hole would not be curved to any extreme degree. You probably wouldn't even notice when you crossed over the event horizon. And from the point of view of anything falling into a black hole, it always takes a finite amount of time to fall to the singularity. And anything which fell in before you would have got to the singularity before you.
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